1. Field of Invention
The present invention relates to a vertical organic transistor and a method of fabricating the same. More particularly, the present invention relates to a vertical organic transistor having a base contact layer made of no less than two hetero materials and a method of fabricating the same.
2. Description of Related Art
Compared with conventional inorganic electronic devices (Si- and GaAs- based electronic devices), the most striking feature of organic electronic devices is low dependency on the substrate. That is, an organic electronic device can be fabricated on a flexible substrate and applied in fabricating a flexible flat panel display. And a low-priced printing technique can be used in fabricating organic electronic devices, and they have the characteristic of being able to be fabricated at a low temperature (<200° C.). Therefore, organic electronic devices are currently directly applied in flexible flat panel displays of large area and low unit price. However, since organic electronic devices have bottlenecks in device properties, even flat panel displays will generally experience problems of low resolution and frame rate, let alone the application of organic transistor devices that operate at Mega Hertz (MHz) and above.
The main technical bottlenecks of the device properties of organic electronic devices are as follows.
1. The mobility of the organic semiconductor serving as a transistor channel is too low. Since the electronic conduction in the organic semiconductor material achieves the object of conducting current by hopping among empty delocalized molecular orbitals between organic molecules under an applied electric field, compared with the high mobility caused by the electrons in the inorganic semiconductor accelerating among periodical potentials, the mobility of the organic semiconductor material is naturally lower than that of Si, GaAs, and so on. Additionally, because (a) most organic semiconductors have characteristics similar to those of the P type semiconductor and (b) the grain boundary of the organic transistor blocks the electronic conduction mechanism, currently the highest hole mobility is about 1 cm2V−1s−1. And although the HOMO (highest-occupied molecular orbital) and LUMO (lowest-unoccupied molecular orbital) of the organic semiconductor are similar to the valence band and conductive band of the semiconductor, since the HOMO and LUMO are still in the stage of molecular orbital (MO), the level density thereof is still much lower than that of a common semiconductor. Therefore, most attempts to fabricate an N type organic semiconductor have achieved no breakthrough.
2. It is too difficult to be integrated into a mature fabricating process. Since most organic semiconductor materials can easily reacted with chemicals commonly used in the semiconductor industry and changed, conventional fabrication methods cannot be adopted in preparing such organic semiconductor materials. And after this fabricating process, further fabricating processes for enhancing device properties can not be performed. Therefore, most research of organic transistors is currently limited to simple bottom gate/source/drain contact layer/organic semiconductors or a bottom gate/organic semiconductor/source/drain contact layer structure. Thus, not only are the device properties limited, but the research of complex hetero structures is also held back.
In view of the above, a vertical organic transistor having the vertical structure is provided. However, because it is difficult to hold the material properties of the vertical organic transistor, device properties such as the output current and lon/loff rate of the transistor are not good enough.